Deformable Silver Coated PMMA Microsphere Spacers

Silver Coated Glass Microspheres work well for increasing the conductivity of bond lines, but they lack the capability to deform when compressed to give increased conductive contact between the surfaces of the bond line. These newly released Silver Coated PMMA Microspheres offer the low weight deformable pmma cores, and 250nm thick silver coating for high conductivity.

Conductivity of this product has been measured at <0.5ohm per square with a 30% by volume preparation. Sizes available cover both the common 50 micron (45-53um) and 100 micron (90-106um) sizes and many others.

These spheres are perfect for producing anisotropic (only conductive in one direction) conductive bond lines.

Actual bond line thickness achieved will be a function of the assembly pressure and the size spheres selected.

In addition to being high conductive these silver coated PMMA is bio-compatible.

Cospheric offers unique capability to manufacture Janus microspheres and microparticles with partial coatings and dual functionality. Currently half-shell or hemispherical coatings can be applied to any sphere (glass, polymer, ceramic) in sizes 45micron in diameter and higher. Coatings can be customized for any color and coverage of between 20% to 60% of the sphere. Each coating is custom formulated for color, charge, magnetic, electric, and surface properties, and solvent resistance per customers’ needs.

Hemispherical coatings of less than 1 micron with tolerances as low as 0.25 micron have been routinely demonstrated. Color combinations are truly unlimited. White, black, silver, blue, green, red, yellow, brown, purple as well as transparent microspheres have been made. Sphericity of greater than 90% and custom particle size ranges are offered.

Optically anisotropic spheres and janus particles with magnetic half-shells have been originally developed for applications in electronic displays, such as e-paper, but are now widely used in numerous applications in diagnostics, medical research, microscopy and biotechnology, as well as electronics, due to their ability to orient themselves in response to electromagnetic field and show a visual response. This is achieved by making spheres both bipolar and bichromal, with dipole precisely aligned with two differently colored hemispheres. As the spheres align themselves, the viewer will observe the color of one hemisphere, while the other hemisphere will be hidden from view, providing an obvious strong visible indication of the presence of the field or other stimuli. In alternating electromagnetic field, these microspheres have been proven to spin at hundreds of times per second.

Calculating microspheres per gram

During scientific experiment design and analysis it is common to need to know the number of spheres per gram of dry material. We have put together the table below to help speed up the process.

If you have material of a density different from those listed in the table, divide the number of spheres per gram in the density ~1.0 g/cc column by the true particle density of your material to get an estimate of the number of spheres per gram.

Product Size

Polyethylene
Density ~1.0 (g/cc)

Soda Lime Glass
Density ~2.5 (g/cc)

Lower (um)

Upper (um)

Spheres per Gram

Spheres Per Gram

20

27

147,162,715

58,630,564

27

32

74,393,558

29,638,868

32

45

33,467,185

13,333,540

45

53

16,233,536

6,467,544

53

63

9,788,528

3,899,812

63

75

5,813,720

2,316,223

75

90

3,401,258

1,355,083

90

106

2,029,192

808,443

106

125

1,239,525

493,835

125

150

734,672

292,698

150

180

425,157

169,385

180

212

253,649

101,055

212

250

154,941

61,729

250

300

91,834

36,587

300

355

54,371

21,662

355

425

32,196

12,827

425

500

19,305

7,691

500

600

11,479

4,573

600

710

6,796

2,708

710

850

4,025

1,603

850

1000

2,413

961

1180

1400

890

354

1400

1700

513

204

1700

2000

302

120

2000

2360

184

73

2360

2800

111

44

2800

3350

66

26

Note: This table assumes the mean diameter is half way between the upper and lower size.

BioCompatability of Metal Coated Spheres

For those scientists who are looking to use silver coated materials such as silver coated microspheres in biomedical applications, it is important to understand whether they are bio-compatable. A selection of abstracts and article references related to the biocompatability of silver follow:

The experiments reported have referred to some of the characteristics of the biocompatibility of Ag. Silver has been shown to display interactions with albumin, as an example of a plasma protein, quite different from those of most metals. Such studies shed further light on the complex issue of protein adsorption on biomaterials. It has also been demonstrated that Ag at concentrations < 1 ppm exerts a considerable influence on the activity of lactate dehydrogenase, this effect being reversed in the presence of albumin. A significant but transient increase in blood levels of Ag following intramuscular implantation of the metal has been observed. This is not reflected in any raised urine level. It is proposed that the richly vascular tissue immediately surrounding the implant in the acute phase of the response gives rise to the transient increase, but a subsequent decrease in vascularity reduces this possibility. It appears that Ag released from implants following this initial period substantially remains in the local area.2

Lack of toxicologocial side-effects in silver-coated megaprostheses in humans1

Deep infection of megaprostheses remains a serious complication in orthopedic tumor surgery. Furthermore, reinfection gets a raising problem in revision surgery of patients suffering from infections associated with primary endoprosthetic replacement of the knee and hip joint. These patients will need many revision surgeries and in some cases even an amputation is inevitable. Silver-coated medical devices proved their effectiveness on reducing infections, but toxic side-effects concerning some silver applications have been described as well. Our study reports about a silver-coated megaprosthesis for the first time and can exclude side-effects of silver-coated orthopedic implants in humans. The silver-levels in the blood did not exceed 56.4 parts per billion (ppb) and can be considered as non-toxic. Additionally we could exclude significant changes in liver and kidney functions measured by laboratory values. Histopathologic examination of the periprosthetic environment in two patients showed no signs of foreign body granulomas or chronic inflammation, despite distant effective silver concentrations up to 1626 ppb directly related to the prosthetic surface. In conclusion the silver-coated megaprosthesis allowed a release of silver without showing any local or systemic side-effects.1

Specific Article References for the biocompatability of silver are below: See the References

Metal Coated Microspheres – Conductive Silver Coating

From early days engineers have been looking for ways to shield circuits from electromagnetic interference (EMI). One of the most effective methods of shielding is by creating an electrically conductive enclosure around the circuit or device. This can be accomplished by using any electrically conductive material. Advances in coated microspheres have enabled the creation of light weight electrically conductive coatings that provide excellent EMI shielding.

Electrically conductive microspheres are produced by applying a metallic silver coating to the surface of the microspheres, thus giving the advantages of a metal particle with the additional properties of the core microsphere. Typically hollow glass microspheres are silver coated as this offers the combination of a low density filler and a conductive particle. Coatings with EMI shielding of greater than 45db have been produced by adding as little as 20% by weight of M-18 silver coated microspheres.